Tap terminating on a listed combination starter

[corvalan]

Situation:

10 feet tap rule ending on a single instantaneous trip over current protection device.

Details:

1: Ampacity of the No. 1/0 AWG tap conductor (150 A) is more than 1/10 the ampere rating (1,200 A) of the upstream OCPD.

2: The tap conductor is physically well protected.

3: The tap conductor doesn't leave the enclosure where it arrives.

4: The tap conductor terminates on an enclosure with an ampere rating less than the ampacity of the tap conductor.

5: The tap conductor terminates on an instantaneous trip breaker (ITB). The ITB has only magnetic trip. The enclosure where this ITB is installed is listed motor combination starter enclosure. The nominal ampere rating of this ITB is 250 A and its pick-up is set to 600A.

6: The motor size protected by the ITB is 50HP @ 460V with a FLA of 65 A. Therefore the ITB is properly sized for this motor.

Question:

1: Is this tap conductor properly applied according to the NEC?

1.a) Which ampere rating should be the tap conductor be applied, the nominal 250 A or the actual PU amps determined by the settings of the ITB (600 A)?

1.b): If the ampere rating to be compared is not the nominal ampere rating of the ITB (250 A) but the actual PU of 600 A, then then 240.21 (B)(5) is not satisfied. If that is the case, it appears to me that this 10 foot tap rule will never be able to be applied to a set of combination starters fed by a gutter.

 

[kwired]

Motors introduce some special situations in this are sometimes, but I think what you have is acceptable.

With a instantaneous trip breaker you can have what seems to be a pretty small conductor compared to the instantaneous trip setting, but that setting is the short circuit and ground fault protection, overload protection of the conductor is still required and is accomplished by the required motor overload protection.

Now get into something like a fire pump that is supposed to be able to run at locked rotor current levels indefinitely and it can be mind blowing for those that don't ever see that kind of thing.

 

[corvalan]

I am sorry for not explaining this question appropriately. I am concerned that the field 10 foot tap does not meet the NEC requirements for the 10 Foot tap rule if the MCP ampere rating is considered equal to its magnetic trip value of 600 A instead of its nominal ampere rating of 250 A.

So the first question is:

For the 10 foot tap rule, should I consider the PU of 600 A or the nominal ampere rating of 250 A?

Second question is:

If the NEC considers the MCM ampere rating as its Magnetic PU of 600 A instead of its nominal ampere rating of 250 A, then we will never be able to connect a 10 foot tap to a combination starter. I have seen many applications where a gutter feeds many combination staters.

Thanks.

 

[augie47]

I think it's an excellent question. Unfortunately one which I fail to find a definite Code answer.

 

[petersonra]

look at it this way.

The combination starter as a unit is listed to provide branch circuit protection to the motor circuit.

The device being connected to is the combination starter.

 

[corvalan]

I am not concerned about the protection of the motor circuit but of the tap conductor. I do not understand your answer. Sorry.


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[petersonra]

I am not concerned about the protection of the motor circuit but of the tap conductor. I do not understand your answer. Sorry.


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the combination starter protects the tap conductor in exactly the same way as a fuse or circuit breaker does.

 

[corvalan]

Thanks for your answer but the MCP rating is not satisfying the NEC tap rule and nowhere in the NEC says that if the 10 foot tap conductor terminates in a listed combination starter is properly protected.


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[petersonra]

Thanks for your answer but the MCP rating is not satisfying the NEC tap rule and nowhere in the NEC says that if the 10 foot tap conductor terminates in a listed combination starter is properly protected.


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Read carefully what it does say. It does not restrict the termination to fuses or cb.

 

[Smart $]

I guess it's time to join in here... :happyyes:

Take a breath of fresh air then read 240.4(E)(6)...

 

[don_resqcapt19]

I guess it's time to join in here... :happyyes:

Take a breath of fresh air then read 240.4(E)(6)...

And that sends you to 430.53(D) and I don't see anything there that would permit the proposed installation. The closest is list item 3, but that requires that the tap conductors terminate at a manual motor starter or on a "branch circuit protective device".

 

[kwired]

I have not yet read through requirements, but will say you are typically allowed to bend the general overcurrent protection rules with some specific load types - especially motors.

Though there may be some finer details to this application, in general a conductor supplying motors is considered properly protected if it has both short circuit/ground fault protection as well as overload protection. Those two types of protection need not always be from same protection device, and the overload device generally can be at any point in the circuit, instead of being limited to the supply end of the circuit.

 

[Smart $]

And that sends you to 430.53(D) and I don't see anything there that would permit the proposed installation. The closest is list item 3, but that requires that the tap conductors terminate at a manual motor starter or on a "branch circuit protective device".

The ITB is a BC-SC-GFPD, is it not? [430.52]

The tap conductors from the BC (in this case it's a 1,200A branch circuit :blink to the ITB must be not less than one-tenth the tap BC-SC/GFPD rating or setting: 1/0@150A>250A/10 & 1/0@150A>600A/10

Tap conductor length is not more than 10' and suitably protected.


Seems compliant to me... at least on the surface. What I'm wondering about is how the 1/0 taps the 1,200A branch circuit, which is most likely paralleled conductors. To be compliant, the tap must connect to each paralleled conductor.

 

[don_resqcapt19]

The ITB is a BC-SC-GFPD, is it not? [430.52] ...

In the normal sense of the term "branch circuit protective device" I don't see an ITB as being one.

 

[Smart $]

In the normal sense of the term "branch circuit protective device" I don't see an ITB as being one.

Exactly where does Code state this "normal sense"?

In support of my conclusion, 430.52(A) references 430.53(D), and Table 430.52 title specifically states "...Branch-Circuit Short-Circuit and Ground-Fault Protective Devices", in which ITB is a column heading.

 

[don_resqcapt19]

Exactly where does Code state this "normal sense"?

In support of my conclusion, 430.52(A) references 430.53(D), and Table 430.52 title specifically states "...Branch-Circuit Short-Circuit and Ground-Fault Protective Devices", in which ITB is a column heading.

I don't see a reference int 430.52(A) to 430.53(D).
I just see a difference in the term "branch-circuit short-circuit and ground-fault protective device" used in 430.52 and the term "branch-circuit protective device" used in 430.53(D)(3). (actually taking another look, 430.53 does not even apply to the question in this thread)

Obviously I must be incorrect as using a tap conductor to feed a motor starter is a common application.

I am not sure what really applies to the conductors in question as they are not branch circuit conductors.

 

[Smart $]

I don't see a reference int 430.52(A) to 430.53(D).

You are correct. I mistook the reference to 430.52(D)

I just see a difference in the term "branch-circuit short-circuit and ground-fault protective device" used in 430.52 and the term "branch-circuit protective device" used in 430.53(D)(3).

I understand your point of view, even though mine differs. Continued below...

(actually taking another look, 430.53 does not even apply to the question in this thread)

Obviously I must be incorrect as using a tap conductor to feed a motor starter is a common application.

I am not sure what really applies to the conductors in question as they are not branch circuit conductors.

Article 430 definitely blurs the line between feeder and branch circuit conductors by definition. We can see 210.2 directs us to 430 for motor [branch] circuits. There is no equivalent in Article 215 for any application. Yet we have Article 430, Part V covering motor feeder short-circuit and ground-fault protection, which applies to any feeder which supplies a motor load. As such, all protection devices between the service entrance and any single motor are deemed short-circuit and ground fault protection devices with respect to the motor being supplied.

 

[david luchini]

(actually taking another look, 430.53 does not even apply to the question in this thread)

Obviously I must be incorrect as using a tap conductor to feed a motor starter is a common application.

I am not sure what really applies to the conductors in question as they are not branch circuit conductors.

I agree...430.28 would seem to be the section that applies. The described install looks like it complies with 430.28(1) to me.

 

[Smart $]

I agree...430.28 would seem to be the section that applies. The described install looks like it complies with 430.28(1) to me.

Hmmm... seems like 240.4(E)(6) should send one to 430.28 rather than 430.53(D) if that's the case. Both sections appear to implement the same requirement with different wording.

 

[david luchini]

Hmmm... seems like 240.4(E)(6) should send one to 430.28 rather than 430.53(D) if that's the case. Both sections appear to implement the same requirement with different wording.

240.4(E)(6) seems superfluous to me, I don't know what the thinking was.

240.4(E)(3) directs you to 240.21, and 240.21(F) directs you to 430.28 and 430.53 for motor feeders and motor branch circuits.

Why the specific reference to 430.53(D) when there is already a reference to 430.53 in its entirety.